Vehicle front structure, activation controller for occupant protection apparatus, and method of production of vehicle front structure

ABSTRACT

A vehicle front structure of the present invention has a pair of side members longitudinally located on right and left sides of a vehicle, and a pair of sub side members juxtaposed to the respective side members and adapted to receive a impact load in the event of a frontal collision after the side members receive the impact load. In this vehicle front structure, the side members first receive the impact load and then the sub side members juxtaposed to the side members also receive the impact load after a certain interval, in collaboration with the side members. Therefore, vehicle deceleration increases in two stages. Since the vehicle front structure has such sub side members, the magnitude of deceleration in the second stage upon collision can be made greater than that in the first stage, and it becomes feasible to make a decision on activation of occupant protection apparatus well.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle front structure, anactivation controller for occupant protection apparatus, and a method ofproduction of the vehicle front structure.

2. Related Background Art

In these years, there is a known vehicle front structure in which abumper reinforcement (hereinafter referred to as a bumper R/F) issupported at the front ends of side members located on right and leftsides of a vehicle and in which, in the event that the vehicle collideswith an obstacle at the bumper R/F first, the side members will undergocompressive deformation to absorb the impact.

For example, Japanese Patent Application Laid-Open No. 2002-2528discloses a body structure for absorbing the impact by deformation ofthe side members. In this body structure, a chassis cross memberextending laterally is provided below the right and left front sidemembers. Connections between arms extending upward from the chassiscross member, and the front side members are arranged as separable inthe event of collision, so as to properly deform the front side members.

On the other hand, more and more vehicles are being equipped withoccupant protection apparatus such as airbags in recent years. When sucha vehicle runs into an obstacle at high speed, i.e., when thedeceleration of the vehicle exceeds a certain preset level, the occupantprotection apparatus is activated to protect occupants.

FIG. 8A and FIG. 8B show an example of graphs showing temporal changesof deceleration (negative acceleration) of a vehicle. FIG. 8A shows thevehicle deceleration upon a collision at low speed, and FIG. 8B thevehicle deceleration upon a collision at high speed. An activationdetermination method for the occupant protection apparatus is, forexample, a method of setting a determination area A in the graphs shownin FIGS. 8A and 8B and activating the occupant protection apparatus whenthe deceleration reaches the determination area A.

SUMMARY OF THE INVENTION

In order to determine more accurately whether the activation of theoccupant protection apparatus is necessary, it is preferable to adoptsuch a vehicle structure that, after an increase of the deceleration inthe initial stage (first stage P₁), the deceleration further increasesin the next stage (second stage P₂), as shown in FIGS. 8A and 8B, and tomake a decision on the activation of the occupant protection apparatus,based on the magnitude and time of the deceleration in the second stageP₂. However, the body structure disclosed in the aforementioned JapanesePatent Application fails to involve consideration to this point.

The present invention has been accomplished in order to solve the aboveproblem and an object of the invention is to provide a vehicle frontstructure that makes it feasible to make a decision on activation ofoccupant protection apparatus well, and a method of production of thevehicle front structure. Another object of the present invention is toprovide an activation controller for occupant protection apparatuscapable of accurately determining whether activation of the occupantprotection apparatus is necessary, by utilizing the vehicle frontstructure.

A vehicle front structure according to the present invention ischaracterized by comprising a pair of side members longitudinallylocated on right and left sides of a vehicle; and a pair of sub sidemembers juxtaposed to the respective side members and adapted to receivea impact load in the event of a frontal collision after the side membersreceive the impact load. In this vehicle front structure, the sidemembers first receive the impact load and then the sub side membersjuxtaposed to the side members also receive the impact load after acertain interval, in collaboration with the side members. Therefore, thevehicle deceleration increases in two stages. Since the vehicle frontstructure comprises such sub side members, the magnitude of thedeceleration in the second stage upon collision can be made greater thanthat in the first stage, whereby it becomes feasible to make a decisionon the activation of the occupant protection apparatus well.

Preferably, the sub side members are located below the side members. Inthis configuration, the sub side members can be located without largelyaffecting the contour of the vehicle. In this case, preferably, each subside member is supported by a support member extending downward from theeach side member. Furthermore, preferably, a portion going into contactwith an obstacle upon a collision of the pair of sub side members islocated ahead of the support member.

Preferably, front ends of the pair of side members are located ahead offront ends of the pair of sub side members. In this configuration, it isfeasible to suitably realize the structure in which the sub side membersreceive the impact load after the side members receive the impact load.

Preferably, the front ends of the pair of side members are located apredetermined distance c ahead of the front ends of the pair of sub sidemembers. This predetermined distance c is set based on a long-sidelength d and a short-side length e in a rectangular section of the sidemembers and a long-side length f and a short-side length g in arectangular section of the sub side members. In this case, morepreferably, a bumper reinforcement with a longitudinal width h isattached to the front ends of the pair of side members and a crossmember with a longitudinal width i is attached to the front ends of thepair of sub side members, and the predetermined distance c isrepresented by Eq (i) below:

$\begin{matrix}{{c = {{k\left\{ {{\frac{5}{8}\left( {d + e} \right)} - {\frac{1}{8}\left( {f + g} \right)}} \right\}} - h + i}},{0.5 \leq k \leq 2.}} & (i)\end{matrix}$

In contraction of the side members and the sub side members uponcollision of the vehicle, a contraction distance with a maximum (localmaximum) impact load on each of the side members and the sub sidemembers is correlated with the long-side length and the short-sidelength in the rectangular section of each of the side members and thesub side members. In the above-described vehicle front structure,therefore, the impact load on the sub side members has a first maximumsubstantially at the same time as a second maximum of the impact load onthe side members, and it is thus easy to set the magnitude of thevehicle deceleration in the second stage upon collision greater thanthat in the first stage. This makes it feasible to make a decision onthe activation of the occupant protection apparatus better.

Preferably, a strength F₀ of the side members and a strength F₊ of thesub side members satisfy the following relational expression (ii), usingan error range ±a % of deceleration detecting means for detecting thedeceleration of the vehicle and a distribution range ±b % ofdecelerations among different vehicle types against an identical impactload:

$\begin{matrix}{\frac{F_{+}}{F_{0}} \geq {{\left( {1 + \frac{a}{100}} \right)^{2}\left( {1 + \frac{b}{100}} \right)^{2}} - 1.}} & ({ii})\end{matrix}$

In this configuration, even if the deceleration detecting means haserror and even if the vehicle deceleration upon collision differs amongvehicle types upon an identical collision, the magnitude of thedeceleration in the second stage of the vehicle can be made greater thanthat in the first stage, whereby it is feasible to make a decision onthe activation of the occupant protection apparatus better.

An activation controller for occupant protection apparatus according tothe present invention is set in a vehicle with the vehicle frontstructure described above, and the activation controller comprises:deceleration detecting means for detecting a deceleration of thevehicle; and activation determining means for determining activation ofthe vehicle protection apparatus, based on the deceleration of thevehicle detected by the deceleration detecting means. In this activationcontroller for occupant protection apparatus, the activation determiningmeans is able to accurately determine the timing of activation of theoccupant protection apparatus, based on the magnitude of thedeceleration of the vehicle in the second stage detected by thedeceleration detecting means.

A method of producing a front structure of a vehicle according to thepresent invention is a method of production of a vehicle front structurein a vehicle comprising a pair of side members longitudinally located onright and left sides of the vehicle and a pair of sub side membersjuxtaposed to the respective side members, the method comprising a stepof determining a location of front ends of the sub side members relativeto front ends of the side members, based on a change of vehicledeceleration due to deformation of the side members and a change ofvehicle deceleration due to deformation of the sub side members in theevent of a frontal collision of the vehicle. Furthermore, preferably,the location of the front ends of the sub side members relative to alocation of the front ends of the side members is determined so that atiming of a second maximum of the vehicle deceleration due to thedeformation of the side members overlaps with a timing of a firstmaximum of the vehicle deceleration due to the deformation of the subside members. This production method of the vehicle front structure canreadily substantialize the vehicle front structure in which themagnitude of the vehicle deceleration in the second stage upon thefrontal collision of the vehicle is greater than that in the firststage.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will beapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an embodiment of the vehicle frontstructure according to the present invention.

FIG. 2 is a side view from the left side of the vehicle front structureshown in FIG. 1.

FIG. 3A is a sectional view along line III—III in FIG. 2.

FIG. 3B is a sectional view along line IV—IV in FIG. 2.

FIG. 4 is a side view showing a state in which a vehicle is running intoan obstacle and in which an impact load is being exerted on the leftside member.

FIG. 5 is a side view showing a state in which a vehicle is running intoan obstacle and in which an impact load is being exerted on the leftside member and on the left sub side member.

FIG. 6A is a graph showing an example of time change of the impact loadexerted on the left side member upon the collision of the vehicle withthe obstacle.

FIG. 6B is a graph showing an example of time change of the impact loadexerted on the left sub side member upon the collision of the vehiclewith the obstacle.

FIG. 6C is a graph showing a time change of vehicle decelerationresulting from application of the impact load to the left side memberand application of the impact load to the left sub side member.

FIG. 7 is a graph showing the magnitudes of impact loads at acontraction distance in a case where the left side member and the leftsub side member receive the respective impact loads to contract.

FIG. 8A is an example of a graph showing a time change of vehicledeceleration upon a collision at low speed.

FIG. 8B is an example of a graph showing a time change of vehicledeceleration upon a collision at high speed.

FIG. 9 is an illustration showing a comparative example of the vehiclefront structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the vehicle front structure, the activationcontroller for occupant protection apparatus, and the production methodof the vehicle front structure according to the present invention willbe described below with reference to the drawings. The same elementswill be denoted by the same reference symbols in the description of thedrawings, without redundant description. It is also noted that thedimensional ratios in the drawings do not always agree with those in thedescription.

FIG. 1 is a perspective view showing an embodiment of the vehicle frontstructure according to the present invention. FIG. 2 is a side view fromthe left side of the vehicle front structure shown in FIG. 1. As shownin FIG. 1 and FIG. 2, vehicle 1 is provided with a left side member 3and a right side member 2. The left side member 3 is located in thelongitudinal direction on the front left side of vehicle 1. The rightside member 2 is located in the longitudinal direction on the frontright side of vehicle 1.

The vehicle 1 is also provided with a bumper R/F 4. The bumper R/F 4 isdisposed in the lateral direction of the vehicle 1. The bumper R/F 4 isfixed near each end thereof to the front ends of the right side member 2and the left side member 3.

The vehicle 1 has a sub frame 5. The sub frame 5 is located below theright side member 2 and the left side member 3, the left front end ofthe sub frame 5 is fixed to the left side member 3 by coupling member10, and the right front end of the sub frame 5 is fixed to the rightside member 2 by coupling member 9. The left rear end of the sub frame 5is directly fixed to the left side member 3, and the right rear end ofthe sub frame 5 directly to the right side member 2. An engine and othercomponents of vehicle 1 are mounted on the sub frame 5.

The vehicle 1 is provided with a left sub side member 7 and a right subside member 6. The left sub side member 7 is juxtaposed to the left sidemember 3. The left sub side member 7 extends nearly in parallel with theleft side member 3 from the left front end of sub frame 5 toward thefront of the vehicle 1, and is supported by a columnar pillar (supportmember) 12 extending downward from the left side member 3. The front endof the left sub side member 7, which is a portion going into contactwith an obstacle upon a collision with the obstacle, is located apredetermined distance c behind the front end of the left side member 3.The front end of the left sub side member 7 is located ahead of thepillar 12. In this configuration, in the event of a frontal collision,only the left side member 3 first receives an impact load and then theleft sub side member 7 receives the impact load, in collaboration withthe left side member 3.

The right sub side member 6 is juxtaposed to the right side member 2.The right sub side member 6 extends nearly in parallel with the rightside member 2 from the right front end of sub frame 5 toward the frontof the vehicle 1 and is supported by a columnar pillar (support member)11 extending downward from the right side member 2. Just as in the caseof the left sub side member 7, the front end of the right sub sidemember 6 is located the predetermined distance c behind the front end ofthe right side member 2. The front end of the right sub side member 6 islocated ahead of the pillar 11.

The vehicle 1 has a cross member 8. The cross member 8 is disposed inthe lateral direction of the vehicle 1. The cross member 8 is fixed neareach end to the front ends of the right sub side member 6 and the leftsub side member 7.

FIG. 3A is a sectional view of the left side member 3 (a cross sectionalong line III—III in FIG. 2). FIG. 3B is a sectional view of the leftsub side member 7 (a cross section along line IV—IV in FIG. 2). As shownin FIGS. 3A and 3B, the left side member 3 and the left sub side member7 are of columnar shape having a rectangular section, the inside ofwhich is hollow. The right side member 2 and the right sub side member 6are also of the same shape as the left side member 3 and the left subside member 7.

As shown in FIG. 2, the vehicle 1 is provided with an airbag sensor 15,a determining device 16, and an airbag module 17. The airbag module 17internally incorporates an airbag, and an inflator for generating a gasto inflate the airbag, and is an occupant protection apparatus forprotecting an occupant in the event of collision. The airbag sensor 15is a deceleration detecting means for detecting the deceleration ofvehicle 1. The airbag sensor 15 detects the deceleration of vehicle 1during normal drives and sends a signal indicating the magnitude ofdeceleration to the determining device 16.

The determining device 16 is an activation determining means fordetermining actuation of the airbag device, based on the deceleration ofvehicle 1 detected by the airbag sensor 15. The determining device 16 isan ECU (Electric Control Unit) and is constructed as internallyincorporating a CPU, a ROM, a RAM, and so on. The ROM stores anactuation determination program and others. The airbag sensor 15 and thedetermining device 16 constitute an activation controller for actuatingthe airbag device (inflating the airbag). The determining device 16decides to actuate the airbag device when the deceleration of vehicle 1from the airbag sensor 15 reaches a predetermined magnitude within agiven time. The determining device 16 actuates the airbag device, forexample, by feeding a signal for actuation of the airbag device to theairbag module 17.

Now, behaviors of the above-described vehicle front structure will bedescribed with reference to FIGS. 4 and 5. FIG. 4 is a side view showinga state in which the vehicle 1 in the present embodiment is running intoan obstacle 20 and in which an impact load is being applied to the leftside member 3. FIG. 5 is a side view showing a state in which thevehicle 1 is running into the obstacle 20 and in which an impact load isbeing applied to the left side member 3 and to the left sub side member7. The description below will concern behaviors of the respectivemembers on the left side in the vehicle front structure, but the memberson the right side also demonstrate behaviors similar to those on theleft side in the event of a full lap collision. Although the left sideof the vehicle will be described as an example, as is also the case inthe description of the production method of the vehicle front structureand others given later, the same also applies to the right side.

As the vehicle 1 is running into obstacle 20, the bumper R/F 4 firstreceives an impact load F1 as shown in FIG. 4. At this time, since abuckling strength (buckling load) of the bumper R/F 4 is higher than anaxial collapse strength (axial collapse load) of the left side member 3,the impact load F1 is transferred to the left side member 3, whereby theleft side member 3 is deformed near the front end to contract. At thistime, the left sub side member 7 is not subjected to any impact loadyet.

Subsequently, when the left side member 3 contracts by the predetermineddistance c (cf. FIG. 2), the cross member 8 also receives an impact loadF2 as shown in FIG. 5. Since a buckling strength. (buckling load) of thecross member 8 is higher than an axial collapse strength (axial collapseload) of the left sub side member 7, the impact load F2 is transferredto the left sub side member 7, whereby the left sub side member 7 isdeformed near the front end to contract.

FIG. 6A is a graph showing an example of time change of the impact loadF1 applied to the left side member 3 upon the collision of the vehicle 1with the obstacle 20. FIG. 6B is a graph showing an example of timechange of the impact load F2 applied to the left sub side member 7 uponthe collision of the vehicle 1 with the obstacle 20. FIG. 6C is a graphshowing a time change of deceleration of the vehicle 1.

As shown in FIG. 6A, the impact load F1 starts increasing immediatelyafter a start of the collision (time t=0), and reaches a value f₁according to the strength of the left side member 3 at a time t=t₁. Whenthe impact load F1 reaches the value f₁, the left side member 3 startsbeing deformed. Thereafter, the impact load F1 repeats increases anddecreases. In this case, a time t=t₂ is defined as a time when theimpact load F1 has a second maximum. On the other hand, as shown in FIG.6B, the impact load F2 starts increasing at a certain constant timeafter the start of the collision (t=0). The reason why the impact loadF2 starts increasing after the lapse of the constant time is that thefront end of the left sub side member 7 is located the predetermineddistance c behind the front end of the left side member 3. When theimpact load F2 reaches a value f₂ according to the strength of the leftsub side member 7, the left sub side member 7 starts being deformed andthereafter the impact load F2 repeats increases and decreases.

As shown in FIGS. 6A and 6B, the time when the impact load F2 firstreaches the value f₂ according to the strength of the left sub sidemember 7 coincides with the time (t=t₂) when the impact load F1 takesthe second maximum. Since the time when the left sub side member 7starts receiving the impact load F2 can be adjusted by theaforementioned predetermined distance c, properly setting thepredetermined distance c enables us to achieve such adjustment that thetime when the impact load F2 first reaches the value f₂ becomes t₂ asshown in FIG. 6B.

When the predetermined distance c is properly set in this way, thedeceleration of the vehicle 1 varies as in the graph shown in FIG. 6C.As shown in FIG. 6C, the deceleration of vehicle 1 comes to have a firststage P₁ with a first maximum at the time t₁. The first stage P₁corresponds to a phenomenon in which the impact load F1 applied to theleft side member 3 first reaches the value f₁. Namely, since at the timet₁ the vehicle 1 receives f₁ as an impact load, the deceleration a₁according to the value f₁ acts on the vehicle 1. Then the decelerationof vehicle 1 comes to have a second stage P₂ with a second maximum atthe time t₂. The second stage P₂ corresponds to a phenomenon in whichthe impact load F1 applied to the left side member 3 again reaches f₁and in which the impact load F2 applied to the left sub side member 7first reaches the value f₂. Namely, since at the time t₂ the vehicle 1receives f₁+f₂ as an impact load, the deceleration a₂ according to thisvalue f₁+f₂ acts on the vehicle 1.

The deceleration a₂ of vehicle 1 at the time t₂ takes a value greaterthan the previously occurring deceleration a₁ by a degree of the impactload value f₂. Accordingly, the deceleration of vehicle 1 in the secondstage P₂ takes a value greater than that in the first stage P₁. Then adeceleration as a criterion for the determination in the determiningdevice 16 shown in FIG. 2 on whether the airbag device should beactuated is set to a value between a₁ and a₂ (e.g., a value b shown inFIG. 6C), whereby the determining device 16 can detect the second stageP₂ of deceleration. The determining device 16 actuates the airbag devicewhen the second stage P₂ of deceleration occurs within a fixed periodfrom a collision.

However, there can be a certain error range (dispersion) in sensitivityof airbag sensor 15 for detecting the deceleration of vehicle 1. In agroup of vehicle types to which a common airbag actuation determinationcriterion is applied, the deceleration upon collision can also slightlydiffer among different vehicle types. On the other hand, thedeceleration of vehicle 1 is determined according to the strengths ofthe left side member 3 and the left sub side member 7. In such cases,therefore, the strengths are set to satisfy Eq (1) below. This makes themagnitude of the deceleration of vehicle 1 in the second stage P₂greater than that in the first stage P₁ even if the airbag sensor 15 haserror and even if the deceleration differs among different vehicle typesin an identical collision mode.

$\begin{matrix}{\frac{F_{+}}{F_{0}} \geq {{\left( {1 + \frac{a}{100}} \right)^{2}\left( {1 + \frac{b}{100}} \right)^{2}} - 1}} & (1)\end{matrix}$

The symbols in Eq (1) above are defined as follows: an error range ofthe airbag sensor 15 is ±a %, a distribution range of deceleration amongdifferent vehicle types in an identical collision mode is ±b %, thestrength (impact collapse load) of the left side member 3 is F₀, and thestrength (impact collapse load) of the left sub side member 7 is F₊.

As described previously, in order to cause the deceleration as shown inFIG. 6C upon the collision of the vehicle 1 with the obstacle 20, it ispreferable to properly set the predetermined distance c. For example,the following two methods can be applied as methods of setting thispredetermined distance c.

The first method is a method of setting the predetermined distance c,based on a long-side length d and a short-side length e in therectangular section of the left side member 3 (cf. FIG. 3A) and based ona long-side length f and a short-side length g in the rectangularsection of the left sub side member 7 (cf. FIG. 3B). FIG. 7 is a graphshowing a relation between contraction distance and impact load in acase where the left side member 3 and the left sub side member 7contract under their respective impact loads F1 and F2. As shown in FIG.7, the impact loads F1 and F2 both repeat increases and decreases (i.e.,vibrate), after contraction (buckling) of the left side member 3 and theleft sub side member 7.

L₁ in FIG. 7 represents a contraction distance of the left side member 3at the second maximum of the impact load F1. When a buckling wavelengthof the left side member 3 is represented by D₁, the distance L₁ isexpressed by Eq (2) below.

$\begin{matrix}{L_{1} = {\frac{5}{4}D_{1}}} & (2)\end{matrix}$

L₂ in FIG. 7 represents a contraction distance of the left sub sidemember 7 at the first maximum of the impact load F2. When the bucklingwavelength of the left sub side member 7 is denoted by D₂, the distanceL₂ is expressed by Eq (3) below.

$\begin{matrix}{L_{2} = {\frac{1}{4}D_{2}}} & (3)\end{matrix}$

In a member with a cross section of rectangular shape, the bucklingwavelength is given by an average of the long-side length and theshort-side length of the rectangular section. Hence Eq (2) and Eq (3)above reduce to Eqs (4) and (5) below, respectively, using the long-sidelength d and the short-side length e of the left side member 3 (cf. FIG.3A) and the long-side length f and the short-side length g of the leftsub side member 7 (cf. FIG. 3B).

$\begin{matrix}{L_{1} = {\frac{5}{8}\left( {d + e} \right)}} & (4) \\{L_{2} = {\frac{1}{8}\left( {f + g} \right)}} & (5)\end{matrix}$

The long side of the rectangular section refers to the longer out of thewidth and height of the left side member 3 (left sub side member 7), andthe short side to the other.

For making the magnitude of deceleration of vehicle 1 in the secondstage P₂ greater than that in the first stage P₁ (cf. FIG. 6C), itsuffices that the contraction position at the second maximum of theimpact load F1 shown in FIG. 7 be made to substantially coincide withthe contraction position at the first maximum of the impact load F2.Namely, all that is required is that the difference between thecontraction distance L₁ of the left side member 3 and the contractiondistance L₂ of the left sub side member 7 should be made tosubstantially coincide with the distance between the collision of thebumper R/F 4 with the obstacle and the collision of the cross member 8with the obstacle. When the predetermined distance c satisfies Eq (6)below, the magnitude of the deceleration of vehicle 1 in the secondstage P₂ becomes larger than that in the first stage P₁.c+h−i=L ₁ −L ₂  (6)

In Eq (6) above, h represents the longitudinal thickness of the bumperR/F 4, and i the longitudinal thickness of the cross member 8. Byarranging Eq (6) above, we obtain Eq (7) below.

$\begin{matrix}{c = {{L_{1} - L_{2} - h + i} = {{\frac{5}{8}\left( {d + e} \right)} - {\frac{1}{8}\left( {f + g} \right)} - h + i}}} & (7)\end{matrix}$

However, the predetermined distance c does not have to precisely satisfyEq (7). For example, where it satisfies Eq (8) below using a constant k(0.5≦k≦2), it is quite possible to make the magnitude of deceleration ofvehicle 1 in the second stage P₂ greater than that in the first stageP₁.

$\begin{matrix}{c = {{k\left\{ {{\frac{5}{8}\left( {d + e} \right)} - {\frac{1}{8}\left( {f + g} \right)}} \right\}} - h + i}} & (8)\end{matrix}$

When the predetermined distance c is set in this manner on the basis ofthe long-side length d and the short-side length e in the cross sectionof the left side member 3 (a section perpendicular to the axialdirection of the member) and the long-side length f and the short-sidelength g in the cross section of the left sub side member 7, themagnitude of deceleration of vehicle 1 in the second stage P₂ can bereadily made larger than that in the first stage P₁.

The second method is a method of setting the predetermined distance c,based on deceleration changes upon collision of the left side member 3and the left sub side member 7. In this method, on the occasion ofproducing the vehicle front structure in the present embodiment, samplesof the left side member 3 and the left sub side member 7 are preparedand signal waveforms indicating deceleration changes upon collision areacquired by experiment. Subsequently, based on the deceleration changesof the left side member 3 and the left sub side member 7, thepredetermined distance c is set so that the timing of the second maximumof deceleration of the left side member 3 overlaps with the timing ofthe first maximum of deceleration of the left sub side member 7, therebydetermining the relative location of the sub side member 7 to the leftside member 3. The term “a timing overlaps with another timing” hereinis not limited to a case where the two timings precisely coincide witheach other, but it also involves a case where the two timings areapproximately coincident with each other.

The vehicle front structure in the present embodiment has the followingeffects. Namely, in the vehicle front structure of the presentembodiment, the side members 2, 3 first receive the impact load and thenthe sub side members 6, 7 juxtaposed to the side members 2, 3 alsoreceive the impact load after a certain interval, in collaboration withthe side members 2, 3. As a result, the deceleration of vehicle 1increases in two stages of the first stage P₁ and the second stage P₂ inthe early period of collision. When the vehicle 1 is equipped with thesub side members 6, 7 in this way, the magnitude of deceleration in thesecond stage P₂ upon collision becomes greater than that in the firststage P₁, whereby it becomes feasible to make a decision on actuation ofthe airbag device well.

A vehicle front structure shown in FIG. 9 is a conceivable comparativeexample of the vehicle front structure to make the magnitude ofdeceleration in the second stage P₂ greater than that in the first stageP₁. FIG. 9 shows only the left side of the vehicle, but a similarstructure is also constructed on the right side of the vehicle. In thisvehicle front structure, a sub frame 37 is provided via coupling member40 and pillar 42 below the side member 33. A bumper R/F 34 is attachedto the distal end of the side member 33, and the bumper R/F 34 firstreceives an impact from the front of the vehicle. The side member 33 hasa deformable zone 33 a with relatively low rigidity near the front endthereof, and in the event of a collision of the vehicle with anobstacle, the deformable zone 33 a is first deformed. Then the firststage P₁ of deceleration appears during deformation of the deformablezone 33 a and then the second stage P₂ demonstrating the decelerationgreater than in the first stage P₁ appears after an end of thedeformation of the deformable zone 33 a.

In the vehicle front structure shown in FIG. 9, however, a part of theside member 33 needs to be made as deformable zone 33 a with lowrigidity. For this reason, the crush stroke upon collision becomeslonger by a degree of absorption of energy reduced by the deformablezone 33 a, which increases the part that has to be repaired. In order todecrease the part that has to be repaired, it is possible to set thelength of the deformable zone 33 a a little longer so as to secure theamount of absorption of energy in the deformable zone 33 a. However,this requires extension of the front overhang and will be subject torestrictions on outside dimensions of the vehicle. Alternatively, inorder to keep the crush stroke short and to avoid the restrictions onthe outside dimensions of the vehicle, it is also possible to increasethe total strength of the side member 33 including the deformable zone33 a. However, the increase in the strength of the side member 33requires a further increase of strength of the compartment zone, so asto largely increase the weight of the vehicle, which is not preferred.

In contrast to it, the vehicle front structure in the present embodimentdoes not need to secure the long crush stroke and does not increase therange that has to be repaired. Since it is unnecessary to increase thelength of the side members 2, 3, there is little influence on theoutside dimensions of the vehicle. Since it can absorb an equivalent orgreater impact energy without need for increase in the strength of sidemembers 2, 3, there is no need for reinforcement of the compartmentzone, which is needed for increase in the strength of side members, andthus an increase in the weight of the vehicle can be minimized.

Since in the vehicle front structure of the present embodiment the sidemembers 2, 3 and the sub side members 6, 7 receive the impact load, theimpact load can be higher than in the case where the impact load isreceived by the side members 2, 3 only. Accordingly, the deceleration inthe initial stage of collision becomes higher on one hand, and thedeceleration in the latter half of collision is reduced on the otherhand, which improves the occupant restraining performance.

In the vehicle front structure of the present embodiment, the sub sidemembers 6, 7 are provided below the side members 2, 3. This permits thesub side members 6, 7 to be placed without largely affecting the contourof the vehicle 1.

In the vehicle front structure of the present embodiment, the front endsof the side members 2, 3 are located ahead of the sub side members 6, 7.This makes it feasible to suitably realize the configuration in which,in the event of the collision of the vehicle 1 with obstacle 20, the subside members 6, 7 receive the impact load after the side members 2, 3receive the impact load.

In the vehicle front structure of the present embodiment, the front endsof the side members. 2, 3 are located the predetermined distance c aheadof the front ends of the sub side members 6, 7. This predetermineddistance c is set based on the long-side length d and the short-sidelength e in the rectangular section of the side members 2, 3 and thelong-side length f and the short-side length g in the rectangularsection of the sub side members 6, 7 as indicated by Eq (7) and Eq (8).

The contraction distance where the impact load F1 becomes maximum incontraction of the side members 2, 3 due to the collision of vehicle 1is correlated with the long-side length d and the short-side length e inthe rectangular section of side members 2, 3. The same also applies tothe contraction distance where the impact load F2 becomes maximum incontraction of the sub side members 6, 7. Therefore, when thepredetermined distance c is set as described above, the impact load F2on the sub side members 6, 7 takes the first maximum almost at the sametime as the second maximum of the impact load F1 on the side members 2,3, and thus the magnitude of deceleration in the second stage P₂ uponcollision can be readily made larger than that in the first stage P₁.This makes it feasible to make a decision on the actuation of the airbagdevice better.

The activation controller for occupant protection apparatus in thepresent embodiment is provided in the vehicle equipped with theabove-stated vehicle front structure and comprises the airbag sensor 15for detecting the deceleration of vehicle 1, and the determining device16 for determining the actuation of the airbag device (airbag module17), based on the deceleration of vehicle 1 detected by the airbagsensor 15. In this activation controller for occupant protectionapparatus, the determining device 16 is able to accurately determine thetiming of actuation of the airbag device, based on the magnitude ofdeceleration of vehicle 1 in the second stage P₂ detected by the airbagsensor 15.

In the production method of the vehicle front structure in the presentembodiment, the location of the sub side members 6, 7 relative to theside members 2, 3 is determined in consideration of the decelerationchanges of the side members 2, 3 and the sub side members 6, 7 uponcollision so that the timing of the second maximum of deceleration ofthe side members 2, 3 overlaps with the timing of the first maximum ofdeceleration of the sub side members 6, 7. Accordingly, it is easy torealize the vehicle front structure in which the magnitude ofdeceleration in the second stage P₂ upon collision of vehicle 1 isgreater than that in the first stage P₁.

With the vehicle front structure of the present invention, it isfeasible to make a decision on the activation of occupant protectionapparatus well. With the production method of the vehicle frontstructure of the present invention, it is feasible to construct thevehicle front structure capable of making a decision on the activationof occupant protection apparatus well. Furthermore, with the activationcontroller for occupant protection apparatus of the present invention, adecision on activation can be accurately made, so that the activation ofthe occupant protection apparatus can be accurately controlled. From theinvention thus described, it will be obvious that the invention may bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

1. A vehicle front structure comprising: a pair of side memberslongitudinally located on right and left sides of a vehicle; a pair ofsub side members juxtaposed to the respective side members and adaptedto receive an impact load in the event of a frontal collision after theside members receive the impact load; wherein front ends of the pair ofside members are located ahead of front ends of the pair of sub sidemembers; wherein the front ends of the pair of side members are locateda predetermined distance (c) ahead of the front ends of the pair of subside members, and wherein the predetermined distance (c) is set based ona long-side length (d) and a short-side length (e) in a rectangularsection of the side members and a long-side length (f) and a short-sidelength (g) in a rectangular section of the sub side members; and whereina bumper reinforcement with a longitudinal width (h) is attached to thefront ends of the pair of side members and a cross member with alongitudinal width (i) is attached to the front ends of the pair of subside members, and wherein the predetermined distance (c) is representedby Eq (i) below: $\begin{matrix}{{c = {{k\left\{ {{\frac{5}{8}\left( {d + e} \right)} - {\frac{1}{8}\left( {f + g} \right)}} \right\}} - h + i}},{0.5 \leq k \leq 2.}} & (i)\end{matrix}$
 2. A vehicle front structure comprising: a pair of sidemembers longitudinally located on right and left sides of a vehicle; apair of sub side members juxtaposed to the respective side members andadapted to receive an impact load in the event of a frontal collisionafter the side members receive the impact load; wherein a strength (F₀)of the side members and a strength (F₊) of the sub side members satisfythe following relational expression (ii), using an error range ±a % ofdeceleration detecting means for detecting the deceleration of thevehicle and a distribution range ±b % of decelerations among differentvehicle types against an identical impact load: $\begin{matrix}{\frac{F_{+}}{F_{0}} \geq {{\left( {1 + \frac{a}{100}} \right)^{2}\left( {1 + \frac{b}{100}} \right)^{2}} - 1.}} & ({ii})\end{matrix}$
 3. A vehicle front structure comprising: a pair of sidemembers longitudinally located on right and left sides of a vehicle; apair of sub side members juxtaposed to the respective side members andadapted to receive an impact load in the event of a frontal collisionafter the side members receive the impact load; wherein a location offront ends of the pair of sub side members relative to a location offront ends of the pair of side members is determined so that a time ofoccurrence of a second maximum of the vehicle deceleration generated byonly the pair of side members in the event of the collisionsubstantially coincides with a time of occurrence of a first maximum ofthe vehicle deceleration generated by only the pair of sub side membersin the event of the collision.
 4. The vehicle front structure accordingto any one of claims 1 to 3, wherein the sub side members are locatedbelow the side members.
 5. The vehicle front structure according to anyone of claims 1 to 3, wherein a bumper reinforcement placed along atransverse direction of the vehicle is attached to front ends of thepair of side members and wherein a cross member placed along thetransverse direction of the vehicle is attached to front ends of thepair of sub side members.
 6. The vehicle front structure according toany one of claims 1 to 3, wherein the vehicle has a sub frame, the subframe being fixed to the pair of side members, and wherein the pair ofsub side members extend from the sub frame.
 7. The vehicle frontstructure according to any one of claims 1 to 3, wherein each sub sidemember is supported by a support member extending downward from the eachside member.
 8. The vehicle front structure according to one of claim 7,wherein a portion going into contact with an obstacle upon a collisionof the pair of sub side members is located ahead of the support member.9. The vehicle front structure according to claim 2 or 3, wherein frontends of the pair of side members are located ahead of front ends of thepair of sub side members.
 10. The vehicle front structure according toclaim 9, wherein the front ends of the pair of side members are locateda predetermined distance (c) ahead of the front ends of the pair of subside members, and wherein the predetermined distance (c) is set based ona long-side length (d) and a short-side length (e) in a rectangularsection of the side members and a long-side length (f) and a short-sidelength (g) in a rectangular section of the sub side members.